1. Field of the Invention
The present invention relates to a method for backing up call charge data, stored in a disk storage, of a telephone switching office, in which individual data blocks are read by the disk storage and transmitted, with write orders, to two sequential mass storages which are independent of one another.
2. Description of the Prior Art
In large telephone switching offices with a large number of subscriber lines, considerable quantities of call charge data are generated; typically, far in excess of 100 Mbyte per day. Because the call charge information has to be further processed quickly in order to be able to bill customers at any time, and because the call charge data has considerable financial importance, it is necessary to store the data periodically on a sequential mass storage; in particular, a tape storage. For security reasons, when this is done the call charge data must be backed up on two tape storages which are independent of one another so that there are, ultimately two copies of the call charge data available.
In order to store call charge data, the current procedure is to first to produce a tape copy of the data which may even consist of a number of tapes, and, after this first backing-up operation has been terminated, a second backup copy of the call charge data of the hard disk is generated on a second tape device.
Because of the abovementioned large quantities of data, the time required to produce a backup copy is in the order of magnitude of hours, often up to ten hours. In addition, of course, the same amount of time is required once more to produce the second backup copy. In view of the fact that backing up is desired or required daily or twice daily, the limits of feasibility is reached. Because the call charge data are usually extracted from a cyclical file, there is the risk of call charge data being lost through overwriting during the long copying times.
An object of the present invention, therefore, is to remedy the abovementioned problems which, to a certain extent, have their origin in the fact that a telephone switching office is a real-time system with a high amount of data flow.
Accordingly, the present invention is directed to a method wherein in each case a data block read by the disk storage is transmitted, together with a write order, both to the first mass storage and to the second or a further mass storage, and after an acknowledgment is received both by the first mass storage and by the second mass storage, the next data block read by the disk storage is transmitted, together with write orders, to both mass storages.
The present invention provides, inter alia, the advantage that the data only has to be read one single time from the hard disk, with the result that the system is considerably relieved as a result of the corresponding reduction in disk access operations. Because the two mass storages, for example tape devices, can execute the write order independently of one another, yet simultaneously, it is not necessary to wait twice for the individual write orders to be terminated. Overall, it is possible to produce two identical backup copies with significantly reduced expenditure in terms of the system and in terms of time. That is, a reduction by almost half can be achieved here.
In order to reduce the time requirements, it is also preferred if the write orders are transmitted simultaneously with the data blocks to both mass storages.
In order to permit backing up of data even when a mass storage is faulty, it is possible to provide that when there is a fault message from one of the two mass storages which is faulty, the individual data blocks are successfully transmitted, with the write orders, to the non-faulty mass storage.
Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Preferred Embodiments and the Drawings.